There's a road off the I84, about 13 miles east of Boise, called Blacks Creek Road. If you travel north on this road, from the freeway, until it turns to dirt, turn left at the fork (about three miles past the end of the tarmac) then you will come upon several short roads which deviate from the main thoroughfare. One of these, which deviates to the right just as you pass an outhouse on the left, stops only a few yards from the main road. If you park there you can walk through the gate and take the trail all the way to Mountain Home if you choose. There are many nice spots to stop and camp.
Also, Open Carry is unregulatable per the Idaho State Constitution, Article 1, Section 11. So, don't worry about open carrying, just do it.